1. Field of Invention
The present invention relates generally to digital image capturing and processing scanners of ultra-compact design capable of reading bar code symbols in point-of-sale (POS) and other demanding scanning environments.
2. Brief Description of the State of Knowledge in the Art
The use of bar code symbols for product and article identification is well known in the art. Presently, various types of bar code symbol scanners have been developed for reading bar code symbols at retail points of sale (POS). In general, these bar code symbol readers can be classified into two (2) distinct classes.
The first class of bar code symbol reader uses a focused light beam, typically a focused laser beam, to sequentially scan the bars and spaces of a bar code symbol to be read. This type of bar code symbol scanner is commonly called a “flying spot” scanner as the focused laser beam appears as “a spot of light that flies” across the bar code symbol being read. In general, laser bar code symbol scanners are sub-classified further by the type of mechanism used to focus and scan the laser beam across bar code symbols.
The second class of bar code symbol readers simultaneously illuminate all of the bars and spaces of a bar code symbol with light of a specific wavelength(s) in order to capture an image thereof for recognition and decoding purposes.
The majority of laser scanners in the first class employ lenses and moving (i.e. rotating or oscillating) mirrors and/or other optical elements in order to focus and scan laser beams across bar code symbols during code symbol reading operations. Examples of hand-held laser scanning bar code readers are described in U.S. Pat. Nos. 7,007,849 and 7,028,904, incorporated herein by reference in its entirety. Examples of laser scanning presentation bar code readers are described in U.S. Pat. No. 5,557,093, incorporated herein by reference in its entirety. Other examples of bar code symbol readers using multiple laser scanning mechanisms are described in U.S. Pat. No. 5,019,714, incorporated herein by reference in its entirety.
In demanding retail environments, such as supermarkets and high-volume department stores, where high check-out throughput is critical to achieving store profitability and customer satisfaction, it is common for laser scanning bar code reading systems to have both bottom and side-scanning windows to enable highly aggressive scanner performance. In such systems, the cashier need only drag a bar coded product past these scanning windows for the bar code thereon to be automatically read with minimal assistance of the cashier or checkout personal. Such dual scanning window systems are typically referred to as “bioptical” laser scanning systems as such systems employ two sets of optics disposed behind the bottom and side-scanning windows thereof. Examples of polygon-based bioptical laser scanning systems are disclosed in U.S. Pat. Nos. 4,229,588; 4,652,732 and 6,814,292; each incorporated herein by reference in its entirety.
Commercial examples of bioptical laser scanners include: the PSC 8500-6-sided laser based scanning by PSC Inc.; PSC 8100/8200, 5-sided laser based scanning by PSC Inc.; the NCR 7876-6-sided laser based scanning by NCR; the NCR7872, 5-sided laser based scanning by NCR; and the MS232x Stratos®H, and MS2122 Stratos® E Stratos 6 sided laser based scanning systems by Metrologic Instruments, Inc., and the MS2200 Stratos®S 5-sided laser based scanning system by Metrologic Instruments, Inc.
In general, prior art bioptical laser scanning systems are generally more aggressive that conventional single scanning window systems. However, while prior art bioptical scanning systems represent a technological advance over most single scanning window system, prior art bioptical scanning systems in general suffer from various shortcomings and drawbacks. In particular, the scanning coverage and performance of prior art bioptical laser scanning systems are not optimized. These system are generally expensive to manufacture by virtue of the large number of optical components presently required to construct such laser scanning systems. Also, they require heavy and expensive motors which consume significant amounts of electrical power and generate significant amounts of heat.
In the second class of bar code symbol readers, early forms of linear imaging scanners were commonly known as CCD scanners because they used CCD image detectors to detect images of the bar code symbols being read. Examples of such scanners are disclosed in U.S. Pat. Nos. 4,282,425, and 4,570,057.
In more recent times, hand-held imaging-based bar code readers employing area-type image sensing arrays based on CCD and CMOS sensor technologies have gained increasing popularity.
In Applicants' WIPO Publication No. WO 2005/050390, entitled “HAND-SUPPORTABLE IMAGING-BASED BAR CODE SYMBOL READER SUPPORTING NARROW-AREA AND WIDE-AREA MODES OF ILLUMINATION AND IMAGE CAPTURE”, incorporated herein by reference, a detailed history of hand-hand imaging—based bar code symbol readers is provided, explaining that many problems that had to be overcome to make imaging-based scanners competitive against laser-scanning based bar code readers. Metrologic Instruments' Focus® Hand-Held Imager is representative of an advance in the art which has overcome such historical problems. An advantage of 2D imaging-based bar code symbol readers is that they are omni-directional by nature of image capturing and processing based decode processing software that is commercially available from various vendors.
U.S. Pat. No. 6,766,954 to Barkan et al proposes a combination of linear image sensing arrays in a hand-held unit to form an omni-directional imaging-based bar code symbol reader. However, this hand-held imager has limited application to 1D bar code symbols, and is extremely challenged in reading 2D bar code symbologies at POS applications.
WIPO Publication No. WO 2005/050390 (assigned to Metrologic Instruments Inc.) discloses POS-based digital imaging systems that are triggered to illuminate objects with fields of visible illumination from LED arrays upon the automatic detection of objects within the field of view of such systems using IR-based object detection techniques, and then capture and process digital images thereof so as to read bar code symbols graphically represented in the captured images.
US Patent Publication No. 2006/0180670 to PSC Scanning, Inc. also discloses digital imaging systems for use at the point of sale (POS), which are triggered to illuminate objects with visible illumination upon the detection thereof using IR-based object detection techniques.
U.S. Pat. No. 7,036,735 to Hepworth et al disclose an imaging-based bar code reader, in which both visible (i.e. red) and invisible (i.e. IR) light emitting diodes (LEDs) are driven at different illumination intensity levels during object illumination and image capture operations so as to achieve a desired brightness in captured images, while seeking to avoid discomfort to the user of the bar code reader.
Also, US Patent Publication No. 2006/0113386 to PSC Scanning, Inc. discloses methods of illuminating bar coded objects using pulses of LED-based illumination at a rate in excess of the human flicker fusion frequency, synchronized with the exposures of a digital imager, and even at different wavelengths during sequential frame exposures of the imager. Similarly, the purpose with this approach is to be able to read bar code symbols printed on substrates having different kinds of surface reflectivity characteristics, with the added benefit of being less visible to the human eye.
However, despite the increasing popularity in area-type hand-held and presentation type imaging-based bar code symbol reading systems, and even with such proposed techniques for improved LED-based illumination of objects at POS and like imaging environments, such prior art systems still cannot complete with the performance characteristics of conventional laser scanning bi-optical bar code symbol readers at POS environments. Also, the very nature of digital imaging presents other problems which makes the use of this technique very challenging in many applications.
For example, in high-speed imaging acquisition applications, as would be the case at a retail supermarket, a short exposure time would be desired to avoid motion blurring at the POS station. One know way of reducing the exposure time of the digital image detection array is by increasing the intensity level of the illumination beam used to illuminate the object during illumination and imaging operations. However, at POS environments, the use of high intensity laser illumination levels is not preferred from the point of view of customers, and cashiers alike, because high brightness levels typically cause discomfort and fatigue due to the nature of the human vision system and human perception processes.
And while it is known that IR illumination can be used to form and detect digital images of bar coded labels, the use of infrared illumination degrades the image contrast quality when bar codes are printed on the thermal printing paper. Consequently, low contrast images significantly slows down imaging-based barcode decoding operations, making such operations very challenging, if not impossible at times.
In WIPO Publication No. WO 2002/043195, entitled “PLANAR LASER ILLUMINATION AND IMAGING (PLIIM) SYSTEMS WITH INTEGRATED DESPECKLING MECHANISMS PROVIDED THEREIN”, incorporated herein by reference, Applicants address the issues of using laser illumination in digital imaging barcode reading systems, namely, the inherent problem of optical noise generated by laser speckles in detected digital images. Such speckle pattern noise, as its often called, is caused by random interferences generated by a rough paper surface, ultimately producing signal variations on the order of size of the bars and spaces of the barcode, resulting in inaccurate imaging and poor decoding. Reduction of this noise is highly desirable.
While WIPO Publication No. WO/2002/043195 discloses and teaches many new ways to despeckle a laser illumination beam, there is still a great need for improved techniques for implementing such laser beam despeckling techniques which are reliable in operation, easy and inexpensive to mass produce.
Thus, there is a great need in the art for improved digital image capture and processing systems that are capable of competing with conventional laser scanning bar code readers employed in demanding POS environments, and providing the many advantages offered by imaging-based bar code symbol readers, while avoiding the shortcomings and drawbacks of such prior art systems and methodologies.